The invention is directed to a method and to an apparatus for the independent monitoring of the flow-through quantity and, potentially, of the concentration of a further gas which is added to a respiratory gas in relatively small concentrations.
In the ventilator-controlled or ventilator-enhanced respiration of humans or animals, it can be advantageous, for example given low lung capacity, to add an extremely low concentration of a further gas to the respiratory gas. For example, it has thus been shown that an admixture of nitrogen oxide (NO) in a concentration of 10-100 ppm promotes the blood supply of the alveolae and the lungs.
Further, it can also be desirable to add a gas that does not participate in the gas exchange, such as SF.sub.6, in similarly low concentrations in order, for example, to be able to measure the lung volume with the assistance of this gas. These are only two examples of how it can be desirable under certain circumstances to add an extremely low concentration of an additional gas to the respiratory gas, whereby respiratory gas, in the broadest sense, is intended to cover all gases or gas mixtures here that are employed in respirator treatment or narcosis.
Particularly given the admixture of nitrogen oxide (NO), it must be considered that even small concentrations of this gas are toxic and that the concentration on the order of magnitude of 10-100 ppm must be carefully monitored. Moreover, nitrogen oxide in higher concentrations is unstable together with O.sub.2 and therefore can only stably exist highly diluted, for example as a 1% solution in nitrogen gas. Even given a desired concentration of the nitrogen oxide of 100 ppm and a dilution of 1% in nitrogen gas, the nitrogen oxide/nitrogen gas mixture to be mixed in only amounts to 1% of the remaining respiration gas. The corresponding gas flow lies within standard margins of error for the controlled gas flow of the respiration gas and is practically negligible in comparison thereto.
The concentration for some auxiliary gases could be identified with the assistance of an additional gas analyzer; this, however, would represent considerable added expense.